Bipin Desai has denied the murder charge but admitted to assisting his 85-year-old father, Dhirajlal Desai, commit suicide because he had been depressed and wanted to end his life.
But prosecutor William Boyce told Guildford Crown Court yesterday that it was his intention to disguise the death as natural but came forward with the assisted suicide claim only when it emerged that a post-mortem would be conducted on his father's body and the lethal drugs in his bloodstream would be revealed.
"He knew when he went to work (the next day) that his father was dead. You have to consider what kind of actor he is," Boyce told the court.
The 59-year-old pharmacist admitted giving his father a fruit smoothie containing morphine and later injecting him with a lethal dose of insulin in August 2015. He has pleaded guilty to two counts of theft relating to stealing the two drugs from his workplace, Vaughan James Chemist in Farnham.
The post-mortem examination on his father revealed he had 1,038mg of free morphine per litre of blood in his system when he died.
Boyce told the court that there was no evidence to support Desai's claims about helping to fulfil his father's wishes to die.
"He suffered no debilitating or disabling symptoms. He was not, on the face of it, near death despite his advancing years," he told the jury.
The court was told how Desai had even made breakfast for his father the next day to disguise the killing as a natural death. He called the 999 emergency number and said he had just come home and noticed his father's curtains were closed and the breakfast had remained untouched.
"It was the start of a whole series of protracted lies told by this defendant," the prosecution said.
A few days later, accompanied by his wife Dipti and sons Samir and Nichil, Desai went into a police station to claim that he had assisted his father commit suicide because he had wanted to be "reunited" with his late wife and dog.
"He said over the past four or five days his father had talked about ending his life, about wanting to 'go upstairs' which he took to mean heaven," the prosecution said.
Desai's trial is ongoing at Guildford Crown Court and is expected to conclude by next week.
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